1. Field of the Invention
The present invention relates to a process for forming cobalt nanoparticles and coating these with copper or copper oxide.
2. Description of Related Art
Generally cobalt has been utilized in industrial nanoparticle applications, such as a catalyst as well as a magnetic and electrically conductive or insulation material. It is previously known to prepare nanoparticles of metals, such as of cobalt, by reducing from metal salts, such as in publications WO 2007/144455, Forsman, J.; Tapper, U.; Auvinen, A, & Jokiniemi, J. (“Production of cobalt and nickel particles by hydrogen reduction”. J. Nanoparticle Res. 10 (2008) 745-759) ja Jang, H. D.; Hwang, D. W.; Kim, D Y.; Kim, H. C.; Lee, B. Y. &. Jeong, I. B. (“Preparation of cobalt nanoparticles in the gas phase (I): Kinetics of cobalt dichloride reduction”. J Ind. Eng. Chem. 9 (2003) 407-411).
It is also previously known that copper and cobalt do not mix together. Cobalt has been coated with copper, for example in liquid phase (such as in publications US 20060177660 and Subramanian, Nachal Devi; Balaji, G.; Kumar, Ch.alia S. S. R.; Spivey, James J. Catalysis Today (2009), 147(2), 100-106). Usually other metals are found in nanoparticles with cobalt, especially in catalysts. Other nanoparticles of cobalt and copper mixtures has been prepared among others by ball mill beater (such as in publication Angeles, J.; Velazquez, C.; Calderon, H. A. NSTI Nanotech 2007, Nanotechnology Conference and Trade Show, Santa Clara, Calif., United States. May 20 24 (2007), Volume 4, 273-276). Also nanoparticles of copper oxide has been produced (such as in publication Ghodselahi, T.; Vesaghi, M. A., Sh.afiekbani, A,; Baghizadelh., A.; Lantrieii, M. Applied Surface Science (2008), 255(5, Pt. 2), 2730-2734). Previously nanoparticles coated with another metal or metal oxide has riot been produced by a reduction method of metal chlorides. Such material is not commercially available, wherein for example cobalt particles would be coated with copper.
In the present invention, costs of producing metal nanoparticles and coating thereof are attempted to reduce and the particles produced are attempted to bring in more homogenous and pure form, This way, for example, permeability of high frequency components, such as antennas, can be enhanced in order that they function more efficiently, and their size can be decreased correspondingly. Compared to these commonly used ferrite particles, permeability of the components can be increased more with ferromagnetic materials, such as cobalt. Optionally the copper oxide shell used as the coating increases for its part substantially the electrical conductivity of the particles.
The invention can also be utilized in production of magnetic insulation materials, by means of which antenna structures as well windings printed on circuit boards can be miniatyrized. Different antennas are continuously used increasingly among others in mobile devices and there is a great need for reducing their size.